WordPress, intelligent back link to previous page

back-link.php

/**
 * Returns a URL to the page where user was before this page
 * @param  string $domain        The sites domain name
 * @param  string $exeption_path The path to go to if not referer is not your site
 * @return string                URL string
 */
function pps_back_href($domain, $exeption_path)
{
    // Get the referer, aka where user comes
    $referer = htmlspecialchars($_SERVER['HTTP_REFERER']);
    // Regex pattern
    $match_pattern = "/\$domain/";
    // Has your site name in it
    if (preg_match($match_pattern, $referer)) {
        return $referer;
    } else {
        // Where to go if the referer is not from your domain
        return $domain.'/'.$exeption_path;
    }
}